MySQL5.7 JSON类型使用详解

json是一种轻量级的数据交换格式，采用了独立于语言的文本格式，类似xml，但是比xml简单，易读并且易编写。对机器来说易于解析和生成，并且会减少网络带宽的传输。

    json的格式非常简单：名称/键值。之前mysql版本里面要实现这样的存储，要么用varchar要么用text大文本。 mysql5.7发布后，专门设计了json数据类型以及关于这种类型的检索以及其他函数解析。 我们先看看mysql老版本的json存取。

示例表结构：

create table json_test( 
id int, 
person_desc text 
)engine innodb; 

我们来插入一条记录：

nsert into json_test values (1,'{ 
  "programmers": [{ 
    "firstname": "brett", 
    "lastname": "mclaughlin", 
    "email": "aaaa" 
  }, { 
    "firstname": "jason", 
    "lastname": "hunter", 
    "email": "bbbb" 
  }, { 
    "firstname": "elliotte", 
    "lastname": "harold", 
    "email": "cccc" 
  }], 
  "authors": [{ 
    "firstname": "isaac", 
    "lastname": "asimov", 
    "genre": "sciencefiction" 
  }, { 
    "firstname": "tad", 
    "lastname": "williams", 
    "genre": "fantasy" 
  }, { 
    "firstname": "frank", 
    "lastname": "peretti", 
    "genre": "christianfiction" 
  }], 
  "musicians": [{ 
    "firstname": "eric", 
    "lastname": "clapton", 
    "instrument": "guitar" 
  }, { 
    "firstname": "sergei", 
    "lastname": "rachmaninoff", 
    "instrument": "piano" 
  }] 
}'); 

那一般我们遇到这样来存储json格式的话，只能把这条记录取出来交个应用程序，有应用程序来解析。

现在到了mysql5.7，我们重新修改下表结构：

alter table json_test modify person_desc json; 

先看看插入的这行json数据有哪些key：

mysql> select id,json_keys(person_desc) as "keys" from json_test\g 
*************************** 1. row *************************** 
 id: 1 
keys: ["authors", "musicians", "programmers"] 
 row in set (0.00 sec) 

我们可以看到，里面有三个key，分别为authors，musicians，programmers。那现在找一个key把对应的值拿出来：

mysql> select json_extract(authors,'$.lastname[0]') as 'name', authors from 
  -> ( 
  -> select id,json_extract(person_desc,'$.authors[0][0]') as "authors" from json_test 
  -> union all 
  -> select id,json_extract(person_desc,'$.authors[1][0]') as "authors" from json_test 
  -> union all 
  -> select id,json_extract(person_desc,'$.authors[2][0]') as "authors" from json_test 
  -> ) as t1 
  -> order by name desc\g 
*************************** 1. row *************************** 
  name: "williams" 
authors: {"genre": "fantasy", "lastname": "williams", "firstname": "tad"} 
*************************** 2. row *************************** 
  name: "peretti" 
authors: {"genre": "christianfiction", "lastname": "peretti", "firstname": "frank"} 
*************************** 3. row *************************** 
  name: "asimov" 
authors: {"genre": "sciencefiction", "lastname": "asimov", "firstname": "isaac"} 
3 rows in set (0.00 sec) 

现在来把详细的值罗列出来：

mysql> select 
  -> json_extract(authors,'$.firstname[0]') as "firstname", 
  -> json_extract(authors,'$.lastname[0]') as "lastname", 
  -> json_extract(authors,'$.genre[0]') as "genre" 
  -> from 
  -> ( 
  -> select id,json_extract(person_desc,'$.authors[0]') as "authors" from json 
_test 
  -> ) as t\g 
*************************** 1. row *************************** 
firstname: "isaac" 
 lastname: "asimov" 
  genre: "sciencefiction" 
 row in set (0.00 sec) 

我们进一步来演示把authors 这个key对应的所有对象删掉。

mysql> update json_test 
  -> set person_desc = json_remove(person_desc,'$.authors')\g 
query ok, 1 row affected (0.01 sec) 
rows matched: 1 changed: 1 warnings: 0 

查找下对应的key，发现已经被删除掉了。

mysql> select json_contains_path(person_desc,'all','$.authors') as authors_exist 
s from json_test\g 
*************************** 1. row *************************** 
authors_exists: 0 
 row in set (0.00 sec) 

总结下， 虽然mysql5.7 开始支持json数据类型，但是我建议如果要使用的话，最好是把这样的值取出来，然后在应用程序段来计算，毕竟数据库是用来处理简单数据的。

总结

以上所述是小编给大家介绍的mysql5.7 json类型使用详解，希望对大家有所帮助